Probing black-hole uniqueness on supermassive scales
Aaron Held École Normale Supérieure - PSL
Abstract
To set the stage, I discuss different assumptions about physics beyond GR and resulting expectations about where to look for the breakdown of the Kerr paradigm. In particular, I present counterexamples to the prevailing expectation that deviations from GR are necessarily tied to local curvature scales. This provides a motivation to probe for a potential breakdown of black-hole uniqueness, not just for solar-mass but also for supermassive black holes. I will then focus on how to leverage VLBI observations of light emitted in the accretion disk to probe the stationary and axisymmetric background spacetime. I will detail different assumptions about additional hidden symmetries of the spacetime and how to then systematically parameterize deviations. Within such a parametrization, I will demonstrate a systematic lensing-band framework to exclude spacetimes for which an observed VLBI feature cannot arise from geodesics that traversed the equatorial plane more than once. If time permits, I will also address complimentary tests with solar-mass binaries and possible pathways to achieve stable nonlinear evolution.
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